1. Field of the Invention
The present invention relates to attaching components to each other and in particular connecting together components of a machine, such as a printer, which are made of materials having different coefficients of thermal expansion.
2. A Discussion of the Background Art
When components made of such materials are attached to each other over a substantial extent, the effect of unequal expansion produces tensions and deformations of the components. This effect is exploited in a bimetallic strip to form a simple thermal switch. In machines, such as printers, it is often desirable to use different materials for components which are to be attached to each other, for example a metal for a printer chassis and a plastics material for a vacuum guide. However, this can involve the above-mentioned problems producing distortion, which is extremely disadvantageous for components, such as a printing platen, which define part of the paper path and for which a high degree of planarity is required at all operating temperatures. Furthermore, any changes in the degree of planarity during operation will alter the separation of the printhead and the print mediumxe2x80x94the so-called pen-to-paper distance. This is difficult to monitor and to take appropriate steps to compensate thus leading to dot displacement and consequently a reduction in print quality.
The present invention seeks to overcome or reduce one or more of the above problems.
According to a first aspect of the present invention, there is provided a device comprising at least two components adjoining each other over a length and having different thermal coefficients of expansion, the components being attached to each other by first attachment means at a first position and by second attachment means at a second position, spaced from said first position along said length, the first and second components being relatively fixed at the first position, characterised in that at least a first of the components is formed so that, at the second position, it can move relative to the other component.
The first component is preferably formed at the second position with a limb which connects the second attachment means to the remainder of the first component, the limb being capable of flexing in the direction of said length.
An advantage of such an arrangement is that, apart from flexure of the limb, no other deformation of the components occurs.
The first component may be sub-divided into separate sub-components which are respectively attached to the other component at spacings in the direction of said length. This may constitute an independent aspect of the present invention.
In a preferred embodiment one or both of said components are capable of bowing in a direction perpendicular to the adjoining surfaces of said components and the total amount of bow is equal to or less than 0.02% of said adjoining length.
The total amount of bow is equal to or less than 0.02% over the normal range of operating temperatures of said device.
Thus according to a second aspect of the present invention, there is provided a device comprising at least two components adjoining each other over a length and having different thermal coefficients of expansion characterised in that a first of the components is sub-divided into a plurality of sub-components respectively attached to the other component at spacings in the direction of said length.
According to the third aspect of the present invention there is provided a device comprising first and second components adjoining each other over a length and having different thermal coefficients of expansion, the components being attached to each other at a first position and at a second position, spaced from said first position along said length, characterised in that said first and second attachment positions are relatively displaceable in the direction of said length.
The first component is preferably a vacuum guide for a printer and made of plastics material and the second component is preferably a printer chassis made of another material such as sheet metal.